Lens structure with prisms



Jan. 22, 1935. w. M. THOMAS LENS STRUCTURE w'ITH PRIsMs Filed April 4,1934 Patented 4Jan. 22, 1935 UNITED STATES PATENT OFFICE l 3,988,882LENS STRUCTURE WITH PRIsMs William M. Thomas, Los Angeles, Calif.Application April I4, 1934, Serial No. 718,985

' 6 claims. (c1. iis-16.4)

This application is in part a continuation of clude the possibility ofprojecting these images my co-pending application lentitled Lens strucinsuperimposed relationship. Stated in other ture with prisms filedDecember 5th, 1933, Serial words, corresponding points on the two lm im-N o. 700,964; now Patent Number 1,957,371. ages will not be spaced aconstant distance from 5 My invention relates to a novel lens structureeach other when the focus of the lens system is 5 for use -inconjunction with av camera or other changed, so that any attempt tosuperimpose the photographic apparatus, as well as .to a photoimages bybringing the frames thereof or boundgraphic apparatus including thislens structure aries 0f the image areas into registraticn. aS iS innovel rent-ionship.A The embodiments to be done in the projectionsystem, results in the forhereinafter described vare particularlyapplicable mation of two images rather than a single com- 10 to a systemof taking' still or motion pictures, posite image. It is an Object 0fthe Present i11- though the principles of the invention may be ventionto provide a leIlS Structure including a applied with 'equal facility toa projection syssingle-lens SYStem and a Simple Correcting means temwherein it is desired to superimpose constituwhich not only permits theformation of two ent images. Furthermore, the features vof the images 0nthe film. but Which alSU automatically 15 vinvention are applicable bothto the taking and maintains corresponding portions of these improjectingof black-andt-white pictures and colages spaced a constant distance flOmeach Other ored pictures. regardless of a movement of the lens system toIt is an object of the present invention to 'use change the ObjectiveHeld 0f fOcuS.

a single-lens system.A in front of a ililm and in Even if properlyPositioned lm images are DlO- 20 conjunction with a beam-splittingstructure for duced, attempts to project such images onto forming thelight rays passing through the sinscreens positioned varying distancesfrom the lens gie-lens system into two identicalvbeams, or for SYStemresult in failure unleSS cOmDenSatiIlg combining two light beams so thatthey can be means is D10Vided-f0r bringing the images into moved throughasingle-lens system when used superimposed relationship. Thus, while alens 25 for projection purposes. The use of a single-lens structurecanfbe designed to operate satisfactorily system permits thephotographing of objects in conjunction with a screen at a fixeddistance from a single viewpoint, or the projecting of from theprojector, the images will not be superimages from a single-lens systemyas distinguished, imposed if the screen is moved closer to the profrom aplurality of lensl systems. jector, for instance, and if the focus ofthe lens 30 One. application of the invention is in conjuncsystem iscorrespondingly changed to secure sharp tion with the taking orprojecting of colored moscreen images. If we consider light raysI drawntion pictures. In the additive system of producfrom corresponding pointson the adjacent iilm ing colored pictures, adjacent frames of themoimages, it is necessary that these rays intersect in tion picture iilmare exposed through two or a point on the screen regardless of thedistance 35 more color filters of different color to form colorbetweenthe screen and the lens system. It is an value images. WhemsuohColor-value images object of the present invention to provide a sysareDl'clected through COHeSDOIldiugly `colored tem for accomplishing thisresult automatically filters, the images can be brought into correct asthe focus of the lens system is changed.

40 SuDeImDOSiticn S0 aS t0 ferm a Composite image Following theyprinciples to lbe hereinafter set 40 the @01ers 0f which correspond t0the colors 0f forth, tne'iens structure' of the invention ands thepblectGgmauy photographe@ In the em' particular utility in conjunction withcameras bodlmnt of. the invention 170 be hereinafter de utilizing 16 mm.lm or smaller, wherein lenses terledz only two color filters are use@thollgh it having a focal distance of 2" or vgreater are used.

1S Wlthm the Scope 0f the Present mlentwn to Withla'rger sizes of n1m,orwith smaller focal dis- 45 utilize a larger number of such lters. i Whenprojecting adjacent lmimages so as to cidsgortmn mtz'y'lorm pres form acomposite image,- it is essential that cora mmf sys g s ances respondingpoints on the two images be corre this distortion 1s not sumcientlyapparent to negavSpondinglyv pla-ced with respect to the adjacent tivethe utility of the lens structure with this size of frames or imageareas.v In exposing such images film or evenwith larger sizes of lm.Itis an object 'it has beenlfound that,` in the absence of any of thepresent invention to providealens structure correcting means, a changein focus ofthe lens whichv is particularly applicable to cameras using'.system will change' the spacing of corresponding 16 mm. iilm or smaller,this structure having a points on the adjacent lm images so as toprefocal distance ofv 2" or more. 55

Further objects and advantages of the invention will be made evidenthereinafter.

Fig. 1 is a diagrammatic sectional view illustrating a form of theinvention.

Fig. 2 is a diagrammatic sectional view of a modification.

Referring to Fig. 1 the lens system of my invention is shown inconjunction with a camera including a front wall 10. A film 130 movesfrom one reel to another in any conventional manner, this movement beingeffected frame-by-frame by any suitable film-advancing means not shown.This film moves adjacent an aperture plate 124 including apertures 125and 126 separatedl by a wall 128, these apertures framing the adjacentimages projected onto the film by thelens structure, as will behereinafter described, identical images being simultaneously projectedonto the film on adjacent image areas thereof.

In one type of camera it has been found desirable to advance the film130 frame-by-frame so that each image area or frame thereof is twiceexposed, once through the upper aperture 126 and again through the loweraperture 125. When such a system is used it is clear that the imagesmust be identically positioned with respect to the boundaries of theimage areas or frames, otherwise the image produced by the secondexposure will not be superimposed on the image produced by the firstexposure. Similarly, regardless of whether or not a double-exposuresystem is used, the images must be correspondingly positioned withrespect to their respective frames or image areas -if an attempt islater made to superimpose the adjacent images by simultaneous projectionthereof or Aby other means.

Ithas been found, however, that with conventional lens systemscorresponding points on the adjacent film areas will not be separated aAconstant distance when the object ive field of focus is changed. Thus,while it is possible to design a lens structure which correctlyregisters on the adjacent image areas any object appearing in a givenobjective field of focus, any attempt to change this objective field offocus will result in the formation of images which cannot besuperimposed. The lens system of the present invention automaticallyovercomes this defect.

'In Fig. l I have illustrated a form of -the invention which can besuccessfully used with 16 mm. film or with fllm of even larger size.Here, the

' front wall 10 is shown as including a sleeve 100 carrying bifurcations101 between which is positioned a pinion 102. This pinion is mounted ona shaft extending through the bifurcations and a thumb wheel 103 issecured to this shaft so that by turning the thumb wheel the pinion 102is rotated. This rotation is utilized in moving a barrel 105 in aforward-rearward direction, this barrel having teeth meshing with thepinion 102. Any suitable means not shown may be utilized for preventingany rotation of the barrel with respect to the front wall 10. Thisbarrel contains a singlelens system 106 diagrammatically shown ascomprising lens elements 107, 108, and 109.

The rear end of the barrel 105 carries' a flared portion 110 in which ismounted a suitable prism means. In this form of the invention the prismmeans is of the reflecting type and includes outer.

reflecting surfaces 111 and 112 and inner reflecting surfaces 113 and114. These surfaces may be suitably mirrored if desired or may be sodisposed that total refiection takes place irrespective of any mirroredsurface. The inner reflecting surfaces 113v and 114 may be formed bycutting a suitable groove 116 transversely through the A I inwardlyextending toes are extremely important in this system, in'that theymakepossible the reflection to the film of the total4 light raysrefiected by the inner and outer reflecting surfaces 113 and' 111, and114 and 112 without loss and without distortion. In some instances it ispossible to form the mirrored surfaces independently of any glasstherebetween in which case suitable supports mustl be used for thesesurfaces. The

light rays reflected therebetween will then movel through air ratherthan through a transparent prism material such as glass.

A light ray emanating from a common point in the objective field offocus passing through the lens system 106 will, for instance, bereflected by the inner reiiecting surface 113 so that it reaches theouter reflecting surface 111, being thence reflected to form a ray 120which reaches the film at a point 121. Similarly, a ray coming from thesame point in the objective field of focus will pass through the lenssystem 106 and be refiected by the inner reflecting surface 114,after-which it can-be reflected by the outer reflecting surface v112 toform a ray 122 reaching the film at a point 123.' The points 121 and 123are positioned a t* distance apart substantially equal to thecenterto-center spacing of the adjacent image areas on the film.Similarly,'rays, emanating from any other point in the objective fieldof focus will be reflected to form point images on the film spaced fromeach other a distance substantially equal to the center-to-centerspacing of the image areas or frames whereby two identical images of anyobject in the objective field of focus will be formed on adjacent imageareas of the film.

In order to secure the best results, I have found it necessary to makethe outer end of said prism means adjacent to the lens system and theinner ends of said prism means adjacent to the two film'apertures, planesurfaces and parallel to each other; if, for instance, as was sometimesdone in the prior art -the inner ends of said prism means adjacent tothe double apertures were made convex instead of plane, such convexcurvature would have a tendency to focus the image reflectedtherethrough which would cause distortion of said images. Suchdistortion is eliminated when both front and rear ends of said prismmeans are made plane surfaces and parallel to each other.

In Fig. 1, I have illustrated the rays 120 and 122 as comprising thecentral rays, and it is very desirable that the prism structure be sodesigned that these rays are parallel to each other. Thus, as the prismmeans moves forward with the lens elements to change the objective fieldof focus,

corresponding points of the adjacent image areas will be separated aconstant distance.

It is preferable in this form of the invention to use a septum means forseparating the beams. This can be accomplished by providing a septumnumber 127 extending from a 'point between the toes 117 and 118 to apoint adjacent the film, this septum member usually terminating at adividing wall 128 of a double-aperture plate 124.

In Fig. 2 I show an embodiment of the invention in which the septummeans 127 extends rearwards from the prism means to a position adjacentthe film. In this embodiment the septum means includes septum means 127and'134, spaced end to end, so as to define a space 133 fr a purpose tobe hereinafter described. The septum means 127 is preferably secured tothe camera housing by any suitable means and preferably extends into thegroove 116 in the prism means. The septum 134 may be secured in fixedrelation with the wall 128 of the aperture plate by any suitable means.This septum means acts to separate the two beams formed by the prismmeans. In this embodiment shown in Fig. 2, it is desirable to form aspace 133, so that a shutter 131 or a color filter support 132, or both,may be positioned therein so as to intercept the beams of light passingthrough the prism means.' This embodiment is particularly adapted forthe exposing of color motion pictures wherein the adjacent image areasof the film 130 carry color value images. In accomplishing this resultit is desirable to position a red color filter, for instance, in thepath of the rays reaching one of the image areas, and to position agreen color filter in the path of the rays reaching the other-v imagearea. The film thus carries alternate color images exposed through thesame color or filter.

The positioning of the filter support 132 and the shutter 131 to rotatein the space 133 is well understoodby any one skilled in the art ofcolor photography in the additive system.

It will be clear that the forms of the inven tion shown in Figs. 1 and 2can be used in projection systems as well as in conjunction with acamera. In a projection system it is necessary that light rays passingthrough corresponding points on the adjacent image areas being projectedmust reach the screen at a common point. Stated in other words, inprojecting adjacent image areas, these image areas will respectivelyform constituent images on the screen, butthese constituent images mustbe in exact registration in order to obtain a composite image. Thus, ifthese constituent images are formed by'projecting through color filterscorresponding in color to those used in exposing color-value images onthe film, the resulting composite image will appear in natural colors inaccordance with the principles involved in `the well-known additivesystem of color projection. n. n

It shouldthus be clear that the invention is not limited in utility to ause in conjunction with a camera.

It will be clear that various changes may be made in the forms of theinvention herein shown without departing from the spirit of theinvention. It will also be clear that the invention finds utilityregardless of whether or not color motion pictures are being produced.In the latter connection a double-exposure or double-projectionblack-and-white system permits a distinct saving in the amount of lightnecessary to expose the image areas, as well as in the amount of light gwhich must be passed through each of these areas in projecting.

I claim as my invention:

l. Photographic apparatus for use with a film having adjacent filmareas' comprising, a double aperture lm plate and guide, a barrelmovable towards and away from said film plate containing a single lenssystem composed of one or more lens elements and a reecting system inprism form, said reflecting system being located in said barrel betweensaid lens system and said film, said reflecting system including twoinner reflecting surfaces and two outer reflecting surfaces, said innerreflecting surfaces being disposed in alignment with said lens systemwhereby light rays moving through said lens system are reflected betweensaid inner and outer reflective surfaces, the front and rear areasofsaid prism means being plane surfaces and parallel to each other, meansfor moving said barrel in a forwardrearward direction to change theobjective field of focus of said lens system and holding same fromangular movement to prevent lateral displacement of the images. Y

2. A combination as defined in' claim 1 in which said prism meansdefines a groove bounding said inner reflecting surfaces and in whichsaid prism means includes toes at the rear end of said groove, said toesextending towards each other.

3. A combination as dened in claim l in which said prism means defines agroove bounding said inner reflecting surfaces and in which said prismmeans includes toes at the rear end of said groove, said toes extendingtowards each other and including a septum means terminating adjacent thespace separating said apertures of said double aperture film plate andextending forward between said toes and within said groove bounding saidinner reflecting surfaces of said prism means. f

4. A combination as dened in claim 1 which includes two septum membersin alignment with each other but spaced end to end to dene a space andin which said photographic apparatus includes a shutter and a colorfilter support moving through ,said space, said color filter supportcarrying a plurality of color filters successively intercepting thelight rays passing through said prism means.

5. Photographic apparatus for use with a film having adjacent film areascomprising, a double aperture film plate and guide, a barrel movabletowards and away from said film plate containing a single lens systemcomposed of one or more lens elements and which barrel has a flaredportion containing a reflecting system in prism form, said reflectingsystem being located in said barrel between said lens system and saidfilm, said reflecting system including two inner reflecting surfaces andtwo outer reflecting surfaces, said inner reflecting surfaces beingdisposed in alignment with said lens system whereby light rays movingthrough said lens system are reflected between said inner and outerreflecting surfaces, the

' front and rear areas of said prism means being plane surfaces andparallel to each other, means for moving said barrel in aforward-rearward direction to change the objective field of focus ofsaid lens system and holding same from angular movement to preventlateral displacement of the images.

6. Photographic apparatus for use with a film having adjacent film areascomprising, a double aperture lrn plate and guide, a barrel movabletowards and away from said film plate, containing a single lens systemcomposed of one or more lens elements, and having a flared portioncontaining a reflecting system in prism form, said reflecting systembeing located in said barrel between said lens system and said film,saidreecting system including two inner reflecting surfaces and twoouter reflecting surfaces, said inner reflecting surfaces being disposedin alignment with said lens system whereby light raysv moving throughsaid lens system are reflected between said inner and outer reflectingsurfaces; the said reflecting system dening a groove bounding said innerreflecting surfaces and including toes at the rear end of said groove,said toes extending towards each other.

WELIAM M. THOMAS.

